Generally, solid oxide cells (SOCs) generally include cells designed for different applications, such as solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), or membranes. Due to their common basic structure, the same cell may, for example, be used in SOFC applications as well as in SOEC applications. Since in SOFCs fuel is fed into the cell and converted into power, while in SOECs power is applied to produce fuel, these cells are referred to as ‘reversible’ cells.
Solid oxide fuel cells (SOFCs) are well known in the art and come in various designs. Typical configurations include an electrolyte layer being sandwiched in between two electrodes. During operation, usually at temperatures of about 500° C. to about 1100° C., one electrode is in contact with oxygen or air, while the other electrode is in contact with a fuel gas.
The most common manufacture processes suggested in the prior art comprise the manufacture of single cells. Generally, a support is provided, on which an anode layer is formed in the green, i.e. unsintered state, followed by the application of an electrolyte layer and a second electrode layer in their green state. The so formed half cell is dried and afterwards sintered at temperatures of up to 1600° C., in some cases in a reducing atmosphere.
The sintering step of the green body however disadvantageously leads to several problems. Since the different layers have a different thermal expansion coefficient, the planar shape of the layers tends to bend during sintering, which causes contact problems if said cell is to be used in a cell stack. Cells being deformed cannot be used and are discarded, making mass production very cost and material extensive and so far unpractical for today's industrial requirements.
In EP-A-2104165 it has thus been suggested to use a symmetrical layer arrangement, wherein the two electrode layers sandwiching the electrolyte layer are formed from the same material. Due to said arrangement, thermal stress during sintering reduces the deformation of the body as the outer layers expand and contract at the same rate. However, this type of cell is very restricted to specific materials as the anode and cathode materials in their green state must have the same thermal expansion coefficient.
It has therefore been desired to improve the manufacturing process of solid oxide cells, to avoid material waste and to make the process more cost effective.